1. Field of the Invention
This invention relates to automotive protective devices such as inflatable air bags, side air curtains, or the like. More particularly, the invention relates to a laminated multi-layered woven textile fabric having pre-configured air holding cavities for use in side air curtains, a composite film product having adhesive and sealing properties useful in the manufacture thereof, and a method of manufacturing said product.
2. Description of the Related Art
Currently available safety restraint devices for automotive vehicles include driver and passenger side air bags that are rapidly inflated by a gasxe2x80x94commonly referred to as xe2x80x9cairxe2x80x9dxe2x80x94which is produced by the ignition of a pyrotechnic material at the moment a collision begins. These devices provide a protective barrier between the vehicle occupants and the vehicle structure. Much of the impact of a collision is absorbed by the air bag, thus preventing or substantially lessening the possibility of serious bodily injury to the vehicle occupants. Air bags are typically stored in a collapsed, folded condition in the steering wheel to protect the driver, and in the dashboard to protect a front seat passenger. The automotive industry has recently introduced side air bags that are stored in the back of the front seats or in the rear seats to protect the cabin occupants in the event of a collision occurring on either side of the vehicle. More recently still, a further safety feature that has been made available for passenger vehicles, especially light trucks, sport utility vehicles (SUVs) and minivans, is the side-impact protective inflatable side air curtain that is designed to provide a cushioning effect in the event of side collisions or rollover accidents. These side air curtains are stored uninflated along the roof of the vehicle or in one of the main support pillars of the vehicle. In the event of a collision the side air curtain deploys along the interior side walls of the vehicle cabin, protecting the occupants from serious bodily injury from contact with the vehicle structure (support pillars, etc.) and from broken glass. They must also be designed to prevent the passengers from being thrown from the vehicle in rollover conditions, which is one of the principal dangers in an SUV accident.
Each of these various types of air bags has different design and physical property requirements, such as gas (air) holding ability or, alternatively, permeability, air pressure and volume, and puncture resistance. For example, the driver side and front passenger side air bags, which deploy in about 0.06 seconds, require very little or no gas retention ability since they are designed to inflate and then to deflate almost immediately after inflation. Passenger side air bags require a controlled permeability, which enables them to lose air more gradually, but still remain inflated for only a few seconds. Side air curtains, on the other hand, must retain air pressure and volume for relatively longer periods of time than other types of air bags to protect cabin occupants in rollover accidents, which can take up to 10 seconds or more to complete. Additionally, to be commercially acceptable, all vehicle air restraint devices must have superior packageability and anti-blocking properties, which permits them to be packed into a relatively small space, such as within a steering wheel or a vehicle support pillar, and to deploy instantaneously when needed without the material sticking to itself after being stored for relatively long periods of time, perhaps even years. These and other physical properties are determined in large part by the type of fabric and weave used in the air bag, whether the fabric is knitted, woven or non-woven, and, importantly, the nature of the coatings that are used on the fabric. Coatings of various types are used to seal the fabric of the air bag and make it air holding.
Wherever coated fabrics are used, considerations such as controlling air permeability, air pressure, and volume exist. Adhesion of the coating material to the textile fabric substrate also presents a serious problem that must be addressed. For example, it is generally more difficult to obtain strong adhesion of a coating material to textile fabrics having a smoother surface than it is with fabrics having a rougher surface. Radio frequency (RF) heat sealing techniques cannot be used with some coatings such as silicone rubber (polysiloxane) to form the air bag because this material will not flow at RF heat sealing temperatures. In such cases, air bags are usually made by stitching, a process that will frequently require the addition of an adhesive sealant in the stitched areas to prevent leakage of air. Even with such adhesive sealants, however, some leakage of air occurs at the stitching, which lessens the protective capability of the air bag.
The air holding capability of a side air curtain is critical since it must remain inflated for extended periods of time to protect passengers in automotive accidents involving multiple rollovers. Unlike driver side and passenger side air bags, which are designed to inflate instantaneously and to deflate almost immediately after inflation to avoid injury to the driver and front seat passenger, a side air curtain must be capable of remaining inflated for from about 3 to about 12 seconds, depending upon the size of the air curtain and the size and type of vehicle involved. An average passenger vehicle would require a side air curtain of from about 60 inches to about 120 inches in length measured along the side of the vehicle. A larger vehicle, such as a minivan, would require an even longer side air curtain. The inflation period of a side air curtain should be sufficient to protect the cabin occupants during at least three rollovers, the maximum usually experienced in such incidents.
Side air curtains are also designed to be configured to different sizes and shapes depending upon the type of vehicle in which they are to be deployed. Thus, the size and shape of the air curtain will vary depending upon the make and type of vehicle. For example, a minivan is likely to require a different configuration of side air curtain than an SUV. The distance and location of the vehicle""s support pillars and the height of the vehicle must also be taken into consideration when designing an air curtain. Since side air curtains are relatively large in comparison with driver or passenger side air bags, the gas pressure available for their expansion, which is limited in volume by the amount of pyrotechnic material available, must also be effectively employed. This is accomplished by designing side air curtains that have air holding cavities only where they are needed to protect the passengers. Those areas where no protection is required have no air holding cavities, thus reducing the volume of gas required to inflate the device to the desired pressure. When side air curtains are deployed they may be subjected to extreme pressures within a relatively broad range depending upon their specific location or application. Air bag deployment pressures generally range from about 50 kilopascals (kPa) to about 450 kPa, which corresponds generally to a range of from about 7.4 pounds per square inch (psi) to about 66.2 psi. Accordingly, there is a need for fabric products and methods of construction for air bags that are versatile both in terms of accommodating the demand for varied sizes and shapes, and which will also be relatively light weight and relatively impermeable to fluids under such anticipated pressures.
Typically, an air bag is constructed by joining two or more woven textile fabrics, each of which has been pre-coated with a sealing material to maintain air pressure when the bag is inflated. The pre-coated fabric is configured to the desired shape as, for example, by cutting, and the separate pieces are then sewn or welded together. Frequently, they are both sewn and welded for strength and air holding purposes. Air holding capability in vehicle restraint devices has been accomplished through the application of coatings such as chloroprene and silicone rubber to a textile fabric (e.g., nylon). Menzel, U.S. Pat. No. 5,110,666 discloses a woven nylon fabric coated with polyurethane to provide the desired permeability and retention of inflation gas. Improved polyurethane, acrylic, polyamide, and silicone coatings that are coated in layers on the fabrics have recently been developed. It has been found that adhesion and heat sealing characteristics are greatly improved with such layered coatings. Examples of such coated fabrics and methods of coating such fabrics are disclosed in commonly assigned abandoned applications Ser. Nos. 09/327,244 and 09/327,245, filed Jun. 7, 1999, and U.S. Pat. No. 6,239,046, issued May 29, 2001, the disclosures of which are incorporated herein by reference and made a part of this disclosure. Another example of a greatly improved bonding system is a polyurethane epoxy resin and polysiloxane beaded heat seal, which is disclosed in commonly assigned application Ser. No. 09/452,030, filed Nov. 30, 1999, now U.S. Pat. No. 6,350,709 B1, which is incorporated herein by reference and made a part of this disclosure. Further developments in air bag technology are disclosed in commonly assigned applications, Ser. No. 09/459,768, filed Dec. 13, 1999, now abandoned, in which the inflatable safety device incorporates connective tethers within the restraint device to provide structural support and stiffening when it is inflated, and Ser. No. 09/572,176, filed May 17, 2000, which relates to a sewn fusion seal process for producing air holding vehicle restraint systems such as those disclosed herein, both of which are incorporated herein by reference and made a part of this disclosure.
Shigeta et al., U.S. Pat. No. 5,302,432, discloses a driver side or passenger side air bag, not an air curtain, in which a film of polyolefin resin and a non-woven material is laminated to a woven synthetic fabric, such as nylon. The polyolefin film is laid down on the woven fabric in molten form and, as such, adheres to the fabric. The non-woven material is bonded to the molten resin and forms the outer surface of the device. The purpose of the non-woven material is said to be twofold: to provide for the escape of air after inflation of the bag, and to protect the driver or passenger, as well as the film, from the hot inflation gas. Such a construction would be undesirable in a side air curtain in which air retention at relatively high pressures for relatively long periods of time is required. Further, the woven multi-layered textiles of the present invention have pre-configured air holding cavities, which would be subject to leakage of the molten film through the fabric when coated and cause sticking, which would impede the deployment of the device when needed. Similarly, Kitamura, U.S. Pat. No. 5,707,711, discloses an air bag, not an air curtain, constructed from a seamless tubular woven fabric to which a polymer resin such as polyurethane is laminated to prevent permeation of gases through the surface of the bag. The resin may be applied as a liquid coating or as a film, which is laminated to the fabric by heat and pressure. However, this prior art does not disclose a method by which a pre-configured multi-layered air bag structure, having the desired shape for use in a particular make and size vehicle, can be laminated in one pass with a coating in film form, thus providing an efficient, cost effective means of producing such a bag.
Instead of sewing or welding pre-configured pieces of coated textile fabric, it is much more economical in terms of cost of production and ease of shipping to weave the side air curtains directly on a loom to produce a multi-layered woven product having pre-configured air holding cavities and the size and shape curtain desired in the final product. Pre-configured woven side air curtains require minimal cutting and essentially no joining of separate pieces, and are ready for coating as they come off the loom. Since the multi-layered fabric is woven from uncoated yarn, the curtain must be coated after weaving to impart the desired sealing and adhesive properties to the product. The difficulty inherent in coating a pre-configured multi-layered woven product is that the liquid coating material, e.g. polyurethane, can soak through the outer layers of woven fabric and penetrate the interior of the curtain. When this occurs and the coating hardens with heat and pressure, the sides of the curtain will stick together, preventing or substantially hindering the opening of the air pockets and deployment of the curtain when it is needed. Moreover, in order to make the side air curtain impermeable to air, the coatings require large concentrations of polysiloxane or other rubber-like materials. These produce a very heavy and bulky curtain that is not easily folded and stored when not in use. The present invention provides a laminated pre-configured side air curtain, a multi-layered composite film product that can be used in the lamination process, and a novel lamination process for manufacturing the side air curtain.
This invention relates to an automotive protective device comprising a multi-layered woven textile fabric having pre-configured air holding cavities and a polymeric film laminated to the outer surfaces thereof to make it air tight to very high pressures for extended periods of time. In the process of making the air curtain of this invention, an adhesive polyether polyurethane or polyester polyurethane prime coat layer is first coated onto a pre-configured, multi-layered, woven textile substrate, and then a polymeric film, such as polyamide, polyolefin or polyurethane is laminated thereto. In one embodiment of the invention, the adhesive prime coat layer is applied to the outer surfaces of the multi-layered textile substrate, which can be woven nylon, polyester, or other synthetic fibers, through rotogravure or direct coating and allowed to dry. A solid polymeric film, such as polyamide, polyolefin or polyurethane film, is applied to the prime-coated textile substrate by means of hot film lamination, through the use of heat and pressure. In an alternative embodiment of the invention, a multi-layered composite film product is disclosed, which can be used as a film laminate without the need for first applying a prime coat adhesive layer to the textile substrate. In this connection, the adhesive prime coat and the polymeric film laminate are applied to the textile substrate in a single step via the film laminate itself. The methods and products of this invention thus permit an automotive protective device such as a side air curtain to be pre-configured or prefabricated to numerous varied designs and shapes prior to coating which will result in economies of operation and reduce the cost of manufacturing these devices.